Packet data communications

ABSTRACT

An internet packet comprises a header field, the header field including a field identifying a source address of the internet packet, a field identifying the destination address of the internet packet and a next header field identifying whether an extension header follows the header and a type of the extension header. The extension header indicates a hop-by-hop option header, the hop-by-hop extension header including a router alert option header type indicating that the extension field is optional for a router to read, and a field providing information for a gateway support node of a packet radio system network. A gateway support node is thereby provided with information, which may be required for example to support a mobile internet protocol (IP). However, by providing the router alert option field, a router is not required to read the remainder of the hop-by-hop option field. As a result, a reduction in the performance of the router in routing internet packets, which may have been incurred if the router was required to read all the hop-by-hop extension field can be limited.

FIELD OF THE INVENTION

The present invention relates to internet packets which are communicatedin accordance with an internet protocol to provide an internet packetdata communications system.

In some embodiments the internet packet may find application with theIpv6 internet protocol providing mobile Internet Protocol (IP)functions.

More particularly, embodiments of the present invention find applicationin packet data communications systems, which include packet radionetworks. In one embodiment the packet data network operates inaccordance with the General Packet Radio Service (GPRS) standard.

BACKGROUND OF THE INVENTION

GPRS has been developed to communicate efficiently packets of data toand from mobile nodes using either a 2G (for example GSM) or 3G (forexample UMTS) mobile radio network. GPRS provides support for apacket-orientated service, which attempts to optimise network and radioresources when communicating data packets such as for example internetdata packets.

Generally, the GPRS network will be connected to another packet datatelecommunications network, which may also be connected to furtherpacket data telecommunications networks. The GPRS network includes agateway support node (GGSN) which provides an interface between anexternal packet data communications network and nodes attached to theGPRS network and provides a plurality of bearers for communicatinginternet packets with the nodes.

The Internet Protocol as developed by the Internet Engineering TaskForce (IETF) has become a preferred way of communicating packet data viatelecommunications networks. Whilst version 4 of the Internet Protocol(Ipv4) has been standardised and has been deployed in many fixednetworks, version 6 of the Internet Protocol is being developed in orderto provide improved facilities. Amongst these improved facilities is afacility to communicate data packets to and from mobile nodes, whichroam from a home network to a foreign network during an IP session [1].Generally, following a process known as route optimisation which will bedescribed shortly, a source and a destination address in the header ofIP data packets being sent from and to a Mobile Node (MN) respectivelywill change as a result of the MN roaming to the foreign network.

The MN may be communicating IP data packets with a Correspondent Node(CN) which is attached to a GPRS network, then the GGSN of the GPRSnetwork must be arranged to route the IP data packets via an appropriatebearer to the CN (which itself may be mobile). If the MN roams to aforeign network mid-session then the GGSN must be arranged to route theIP data packets to the CN (mobile user equipment) via the appropriatebearer. The appropriate bearer will have been set up by the GGSN when asession initiation was established at a time when the MN was attached toits home network. As such the parameters for the bearer will have beenestablished with reference a home address of the MN as the sourceaddress. However as explained above, the source address in the header ofthe IP data packets will be changed during the session from the homeaddress of the MN, when attached to its home network, to acare-of-address after the MN roams to the foreign network.

It has previously been proposed in co-pending UK patent applicationnumbers 0226289.7, 0222187.7, 0230336.0, 0222161.2 and 0230335.2 toprovide a mobile node's home address in an extension header field inIPv6 known as the hop-by-hop field. As such the GGSN will be able toidentify the appropriate bearer through which IP data packets can berouted to a correspondent node (CN) attached to the GPRS network,because the MN's home address provides the source address with respectto which the appropriate bearer was set up. However according to theIpv6 standard, if the hop-by-hop filed option is selected then everyrouter along a communications path followed by the internet data packetsfrom an MN to the CN is required to read the mobile's home address inthe hop-by-hop field. This requirement could represent a reduction inperformance of a network formed by the routers, as a result of therouter reading the mobile's home address although this address may notbe relevant to the router.

SUMMARY OF INVENTION

According to the present invention there is provided an internet packetcomprising a header field, the header field including a fieldidentifying a source address of the internet packet, a field identifyingthe destination address of the internet packet and a next header fieldidentifying whether an extension header follows the header and a type ofthe extension header. The extension header indicates a hop-by-hop optionheader, the hop-by-hop extension header including a router alert optionheader indicating that the extension field is optional for a router toread, and a field providing information for a gateway support node of apacket radio system network.

As explained in our co-pending UK patent application number 0226289.7,by providing a home address of a mobile node in the hop-by-hop extensionheader field, inter-working between a gateway support node of a packetradio network and a data communications network when supporting mobileIP functions can be provided. However, if every router in acommunications path between a mobile node and a correspondent node isrequired to read all the data in the hop-by-hop extension header, then asubstantial reduction in performance to a network formed by the routersmay occur. By providing a router alert option field in the hop-by-hopextension header, a relatively short indication that the hop-by-hopfield is providing information to a gateway support node is made andtherefore does not need to be read by a router. As a result any loss inperformance caused by a router having to read the entire hop-by-hopfield can be substantially reduced.

In some embodiments the internet packet is formed in accordance with theIpv6 specification, the routers and the packet radio network beingoperable to support the Ipv6 specification. As such, according to theIpv6 Router Alert Option standard the first three bits of the routeralert option field are set to be zero, any router which does notrecognise this Router Alert Option type will skip the information in thehop-by-hop field. For some applications (explained below) the remainderof the hop-by-hop extension header field may include at least a 128-bitaddress. According to the IP Ipv6 specification defined atwww.ietf.org/rfc/rfc2460.txt [3], the hop-by-hop extension header fieldmust be read and processed by every node along a packet's communicationpath. If a node or router is only required to read a relatively shortfield (three bits) indicating that the rest of the message is onlyrelevant to a gateway support node of a packet radio network, then aperformance penalty for having to read the hop-by-hop extension headerwill be relatively small with respect to having to read the entirehop-by-hop field.

In one example, the gateway support node establishes a packet databearer for communicating internet packets from a mobile node across apacket radio network to a CN attached to the network in accordance witha source address of the internet packets when an IP session was set up.If the source address of internet packets in the basic Ipv6 headerchanges during the session as a result of the mobile node roaming to aforeign network, the gateway support node will not recognise the sourceaddress and will drop the internet packets. The original source address(home address) which was used to establish the bearer across the packetradio network, is known as the home address. By providing the homeaddress in the hop-by-hop extension header the gateway support node willbe able to identify the appropriate bearer even though the sourceaddress of the internet packet in the basic Ipv6 header will havechanged to a care-of-address not known to the gateway support node.

Various further aspects and features of the present invention aredefined in the appended claims. These include a gateway support node, arouter and a method of communicating internet packets.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIG. 1 schematically illustrates an example architecture of a mobileradio network which is arranged to support packet data communications;

FIG. 2 schematically illustrates a mobile node communicating with acorrespondent node via a home network and after roaming to a foreignnetwork performing a route optimisation procedure;

FIG. 3 schematically illustrates example internet packets at differentstages in the route optimisation procedure;

FIG. 4 provides a schematic illustration of parts of a packet radiocommunications network;

FIG. 5 is a schematic illustration of the parts shown in FIG. 4illustrating an operation of a gateway support node to communicatedown-link packets to a correspondent node;

FIG. 6 is a schematic illustration of an internet packet which has beenadapted to provide a router alert header as part of a hop-by-hopextension header, with a field for providing information to the GGSN ofFIG. 2;

FIG. 7 is a flow diagram illustrating the operation of the gatewaysupport node when processing an internet packet in the form illustratedby the example shown in FIG. 6 for a down-link communication;

FIG. 8 is a flow diagram illustrating the operation of the gatewaysupport node when processing an internet packet in the form illustratedby the example shown in FIG. 6 where the GGSN information field includesa source home address;

FIG. 9 is a flow diagram illustrating the operation of a router whenprocessing an internet packet in the form illustrated by the exampleshown in FIG. 6;

FIG. 10 is a schematic illustration of the parts shown in FIG. 4illustrating an operation of a gateway support node for an up-linkcommunication; and

FIG. 11 is a flow diagram illustrating the operation of the gatewaysupport node when processing an internet packet in the form illustratedby the example shown in FIG. 6 for an up-link communication.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Mobile Packet Radio Network Architecture

An example architecture of a packet radio network which is arranged tosupport packet data communications is provided in FIG. 1 and explainedin more detail in Annex 1. To assist in understanding and explaining theembodiments of the present invention and the advantages provided by suchembodiments, a brief description will be provided here. The packet radionetwork presented in FIG. 1 illustrates an arrangement which conforms tothe GPRS/UMTS standard and provides a packet radio network forcommunicating internet data packets with nodes which are attached to thenetwork via terrestrial radio bearers referred to as UTRAN. The packetradio network includes a Gateway GPRS Support Node (GGSN) which isoperable to provide an interface between an external network PDN and thenodes attached to the GPRS/UMTS network. Since the nodes arecommunicating via the UTRAN radio interface they may be generally mobilenodes. However in the following description the mobile user equipment(UE) which are attached to the packet radio network will be referred toas correspondent nodes CN. As will be explained shortly, the GPRS/UMTSnetwork provides a plurality of packet data bearers for communicatinginternet packets from the GGSN to the correspondent nodes CN and fromthe correspondent nodes CN to the GGSN. Typically, packets received fromcorrespondent nodes by the GGSN are allowed to egress from the packetradio network to the external packet communications network PDN. Thesepackets may be destined for other nodes which may be attached to theexternal network PDN or may be attached other networks, the packetsreaching these nodes via the external network PDN.

Mobile Ipv6 Route Optimisation

Route optimisation is a known as part of the internet protocol mobilitystandard version 6 (MIPV6) and may be performed for a node which roamsfrom a home network to a foreign network. The route optimisation is aprocess by which a node, which changes its affiliation from a homenetwork to a foreign network, can be arranged to communicate internetpackets to and from the node via the foreign network without beingrouted via the home network and without requiring a home agent as is thecase for Ipv4. A node which changes its affiliation by roaming from itshome network to a foreign network will be referred to in the followingdescription as a mobile node.

As is conventional with the internet protocol, nodes which communicateinternet packets between each other provide the destination address aswell as the source address in the basic internet packet header. FIG. 2provides an illustration of a route optimisation process between acorrespondent node CN attached to a GPRS network and a mobile node MN.In FIG. 2 the correspondent node CN is communicating internet packets toand from the mobile node MN whilst the correspondent network MN isaffiliated with a GPRS/UMTS network 200. As illustrated by two positionsof the mobile node MN 202, 204, the mobile node which was originallycommunicating internet packets with the correspondent network CN via itshome network 210 moves to a foreign network 212. Thus originally themobile node MN was communicating internet packets via its home agent HA.When the mobile node MN moves from the home network 210 at position 202to a foreign network 212 at position 204 internet packets according to aconventional operation of Ipv4 would have to be routed via the homeagent. That is to say the destination address for packets sent to themobile node MN would be its home address, and the source address ofpackets sent from the mobile node MN would be its home address. As such,internet packets would have to be routed via the foreign network 212 andthe home network 210 to and from the correspondent node CN via theGPRS/UMTS network 200. It will be appreciated that routing packets viathe home agent after the mobile node MN has roamed to the foreignnetwork consumes network resources unnecessarily and further increasesthe delay in communication of the internet packets.

As mentioned above, route optimisation is a process by which internetpackets are communicated between the correspondent node CN and themobile node MN without having to pass through the home agent HA therebyreducing the resources used to communicate the internet packets.Typically a delay in communicating packets is also reduced.

FIGS. 2 and 3 effectively provide a summary of relevant parts of theroute optimisation process, which will be useful in understanding theembodiments of the present invention, which will be described shortly.FIG. 3 provides an example illustration of Internet packet headersbefore and after route optimisation. In FIG. 3 internet packet 300provides an illustration of an internet packet (Ipv6) header to be sentfrom the mobile node MN when attached to the home network at position202 to the correspondent node CN when attached to the GPRS network 200.The Internet packet header 300 includes the address of the correspondentnode CN within a destination field 302 and the home address of themobile node (MN) within a source address field 304. The Internet packetheader 300 also includes a further field known as the hop-by-hop field306 which will be explained shortly. The IP packet 300 for communicationfrom the mobile node (MN) to the correspondent node (CN) is known as adown-link internet packet.

For the up-link, that is to say from the correspondent node CN to themobile node MN, an Internet packet header 310 is shown to include withinthe destination field 312 the home address of the mobile node MN and,within the source address field 314, the address of the correspondentnode CN.

Following route optimisation in accordance with a change of affiliationof the mobile node, the mobile node MN must inform the correspondentnode of its new address. The new address, that is the address to be usedto access the mobile node MN via the foreign network, is known as thecare-of-address. To inform the correspondent node CN of thecare-of-address of the mobile node MN, the mobile node MN sends thecorrespondent node CN a binding update message.

Following the binding update the internet packet header for thedown-link 350 now includes the care-of-address of the mobile node MN inthe source field 352. Correspondingly, the destination field, of theinternet packet sent to the mobile node MN contains the care-of-addressof the mobile node in the internet packet header 360.

Should the CN itself change its affiliation either within the network orto a foreign network then correspondingly a binding update would beperformed by the correspondent node CN. As illustrated in FIG. 2 thecache address store of the mobile node 230 is then updated to includethe care-of-address of the correspondent node CN in association with theaddress of the correspondent node CN with the effect that subsequentInternet packets use the care-of-address of the correspondent node CN inplace of the home address of the correspondent node.

Functions of the GGSN

An example embodiment of the present invention will now be describedwith reference to FIG. 4 which provides elements forming part of theGPRS/UMTS network which appears in FIG. 2. In FIG. 4 a gateway supportnode (GGSN) 400 is shown together with a Serving GPRS Support Node(SGSN) 402 and a Universal Terrestrial Radio Access Network part (UTRAN)404. The GGSN 400, the SGSN 402 and the UTRAN 404 form part of thepacket radio network as represented in FIG. 1 for communicating datapackets to and from mobile User Equipment (UE) 406, which for theillustrative explanation forms the correspondent node CN. The UTRAN 404includes RNCs and Node Bs as represented in FIG. 1 and provides afacility for communicating packets via a radio access interface formedby the Node B with the UE 406.

As will be appreciated in the up-link direction, that is from thecorrespondent node CN 406 to the GGSN, corresponding tunnelling isemployed to route the Internet packets back to the GGSN so that theinternet packet can egress from the GPRS/UMTS network 200 to the foreignnetwork 212. As shown in FIG. 2 a communication path from the MN to theGGSN 400 includes several routers 420, 422, 426 within the foreignnetwork 212.

Also included within the GPRS/UMTS elements shown in FIG. 4 in the GGSN400 is a Traffic Flow Template (TFT) controller 470 and a Service BasedPolicy (SBLP) controller 472. The TFT 470 and the SBLP 472 operate inaccordance with an embodiment of the present invention as will bedescribed shortly to manage the communication of IP data packets fromthe GGSN to the mobile UE (CN) and from the mobile UE (CN) to the GGSNand outward to the foreign network 212.

In the following description the mobile UE 406 forms the correspondentnode CN as represented in FIG. 2, whereas a node from which the UE 406receives internet data packets and sends internet data packets to formsa mobile node which roams to the foreign network 212 as explained withreference to FIG. 2.

In order to provide an explanation of the embodiments of the presentinvention the operation of the TFT controller 470 which is shown in FIG.4 will be briefly described with reference to FIG. 5.

Traffic Flow Template (TFT Based Packet Filtering at the GGSN)

As shown in FIG. 5 the TFT controller 500 which operates in the GGSNmobile IP layer is provided with a list of source addresses 502 whichare used to control the communication of IP data packets in accordancewith a source address included within the Internet packet header. TheTFT 500 arranges to communicate the IP data packets via an appropriatebearer which has been set up using the packet data protocol contextactivation which may be initiated by an application in the UE (CN), oron the mobile node MN and is analogous to logging onto a requireddestination.

To select an appropriate UMTS bearer the GGSN to establish a trafficflow template in accordance with the following parameters:

-   -   IPV4 source address type    -   IPV6 source address type    -   Protocol identifier/next header type    -   Single destination port type    -   Destination port range type    -   Single source port type    -   Source port range type    -   Security perimeter index type    -   Type of service/Traffic class type    -   Flow level type

For each PDP context to be used for a multimedia session a traffic flowtemplate is generated by the mobile terminal and sent to the GGSN whichsubsequently uses this traffic flow template to filter incoming packetsbased on information provided in the template. For example, for packetssent from an Ipv6 mobile node, the correspondent node CN will create atraffic flow template which creates the IP address of the mobile node asthe Ipv6 source address for packets in the down-link direction.

As shown in FIG. 5 an internet packet 504 received from the externalpacket data communications network 212 on: the down-link, forcommunication to the CN 406 may include the address of the correspondentnode CN ADD in the destination address field 506. The internet packetmay include the home address of the mobile node HA of MN in the sourceaddress field 508.

In operation the TFT controller 500 checks the source address of theinternet packet against the list 502 and routes the internet packet viathe appropriate data bearer which has been set up within the TFTcontroller for communicating the Internet packet to the respectivecorrespondent node CN. However, what happens when the mobile networkroams from its home network 210 to the foreign network 212 as shown inFIG. 2?

As explained with reference to FIG. 3, following route optimisation thesource address for the mobile node will be the care-of-address of themobile node. Thus, an Internet packet 510 corresponding to the Internetpacket 504 will be sent from the mobile node to the GGSN forcommunication to the correspondent node CN 406. As shown the IP header510 received from the mobile node MN when attached to the foreignnetwork 212 includes within its destination address field 512 the homeaddress of the correspondent node CN ADD, but within its source addressfield 514 the care-of address of the mobile node C of A MN. The TFT hasa packet bearer, which has been set up and defined for conveying theinternet packets to correspondent nodes in respect of the sourceaddress. However, the internet packet 510 received from the mobile nodeafter it has roamed to the foreign network 212 will not be recognised bythe TFT controller 500 and so the packet will be dropped, unless someadaptation of the GGSN is provided.

Use of the Hop-by-Hop Extension Header Field

A previously proposed solution disclosed in [5] for addressing theinter-working between the TFT controller 500 in the GGSN after routeoptimisation is to include the home address of the mobile node MN withinan extension header field known as the hop-by-hop field 516. Byincluding the home address of the mobile node within the hop-by-hopfield 516, the TFT controller can identify the appropriate bearer, whichshould be used to convey an Internet packet to the correspondent nodeCN. This is the packet bearer, which was set up during a PDP contextactivation as part of a session initiation. Thus, if the mobile noderoams to a foreign network during mid-session then by providing the homeaddress of the mobile node in the hop-by-hop field the TFT controller500 can identify the appropriate bearer to be used to convey theinternet packets to the CN 406. The hop-by-hop address field is alsoknown as the routing header type two (extension to header of IP6packets).

According to the Ipv6 specification [3], the hop-by-hop extension fieldmust be read by each intermediate router. As such, using the hop-by-hopextension header to provide the mobile's home address, will require thateach router along a path communicating the internet packets from themobile node to the correspondent node is required to read the mobile'shome address in the hop-by-hop extension header. This requirement couldrepresent a substantial performance degradation of the IP network,resulting from the requirement to read the mobile's home address in thehop-by-hop extension header.

Use of Router Alert Option for GGSN Information

In order to reduce a degradation in performance resulting from allrouters along the communications path having to read the mobile node'shome address in the hop-by-hop extension header field, an internetpacket according to an embodiment of the invention includes informationrelating to supporting Ipv6 mobility for the GGSN, such as for example arouter alert option in the hop-by-hop extension header which includesthe mobile node's home address. A header for the internet packet isillustrated in FIG. 6.

In FIG. 6, the fields “Version” 601, “Traffic Class” 602, “Flow Label”604, “Payload Length” 606 and “Hop Limit” 608 are as specified in [3]and so will not be explained here, since the reader can refer to [3] forthis information. The “Next Header” field 610 is arranged to specifythat the next header to the present header provides a hop-by-hop option(with a value=0) and so must be read. The “source address” field 612 andthe “destination address” field 614, provide the source and destinationsaddresses as explained with reference to FIG. 3.

The “Next Header” field 616 within the hop-by-hop extension header part618 provides an indication as to whether or not a further header followsthe current extension header. The field “Header Extension Length” 620provides an indication of the length of the extended header if present.

The next fields in the IP packet are specified in accordance with therouter alert option type [4]. The first of these fields provides the“Router Alert Option” field 622. The “Router Alert Option” fieldprovides an indication that the field is for alerting routers and has avalue of zero specified as three bits (000). The next field 624 providesa “hop-by-hop option type” which is set to a value of five by a fieldlength of five bits.

The next field 626 provides a value field and is set to a value toindicate that the information in the remainder of the header is providedfor the GGSN of a GPRS network. This value may be any value which hasnot so far been reserved in the specification [4]. For example the valuemay be “3”. Alternatively, it may be possible to utilise a value alreadyreserved such as “2” meaning “Datagram contains an active networkmessage”. If the definition of the value “2” permits the use of thisvalue for mobility information for the GGSN, then this value may bere-used. Otherwise the next available value which is “3” will be used.The remaining field 628 provides the information to the GGSN.

One example of the information for the GGSN which may be provided in thefield 626 is the mobile node's home address. This provides a 128-bitaddress field. The router alert field in contrast is only 3-bits withthe “hop-by-hop option type” field being only 5-bits. As a result, sinceevery router along the communications path must only read 3-bits todetermine whether the information is relevant to the router concerned, aperformance loss is substantially reduced with respect to a performanceloss which may have occurred if a remaining 128-bit address field wasalso required to be read by every router along the communications path.

Summary of the Operation of the GGSN for TFT

In summary, by analysing the hop-by-hop field in combination with thesource address field the TFT controller 500 can identify the appropriatebearer 520 to communicate the Internet packets to the correspondent nodeCN because the list 502 includes the home address of the mobile node.The operation of the GGSN when receiving IP packets for ingress to thepacket radio network is summarised by the flow diagram of FIG. 7 andexplained as follows:

S1: An internet packet according to the example in FIG. 6 is receivedfrom the external network.

S2: The GGSN detects whether a next header field of the internet packetincludes a hop-by-hop field option. If the GGSN does detect that thenext header field includes a hop-by-hop field option, then processingproceeds to step S3, and otherwise continues from step S6.

S3: If the GGSN detects the hop-by-hop extension header then at step S3the GGSN identifies whether a router alert header type is present,within the hop-by-hop extension header field. In some embodiments thisstep may be omitted.

S4: In step S4, the GGSN recovers information from the field provided inthe hop-by-hop extension header field providing data representing theinformation.

S5: The GGSN then controls egress and/or ingress of internaet packets tothe packet radio network in accordance with the information recovered.

S6: At step S6 the GGSN continues processing with oither functions, theprocessing of the current packet may however continue depending on thecontent of the GGSN information field.

As will be appreciated one of the uses of the field in the hop-by-hopextension header field is to provide a mobile node's home address assource address, so that the TFT can identify the appropriate bearer forcommunicating the internet packet to the correspondent node. For thisexample embodiment the GGSN operates as represented by the flow diagramin FIG. 8 and explained as follows:

S7: The GGSN detects, from either the data provided in the hop-by-hopextension header field for the gateway support node, or the sourceaddress of the internet packet, a source home address of a mobile nodecommunicating the internet packets.

S8: The GGSN determines whether the source address of the internetpacket identifies the packet data bearer for communicating the internetpackets to a correspondent node attached to the packet radio network. Ifthe source address does correspond to a packet data bearer thenprocessing proceeds to step S10, otherwise processing proceeds to stepS9.

S9: The GGSN determines whether the home address provided in the GGSNinformation field identifies the packet data bearer for communicatingthe internet packets to a correspondent node attached to the packetradio network. If the home address does correspond to a packet databearer then processing proceeds to step S10, otherwise at step S11 thepacket is dropped.

S10: The GGSN allows ingress of the internet packets via the identifiedpacket data bearer, or

S11: The GGSN drops the internet packet.

Summary of Router Operation

As will be appreciated, routers along a communications path between themobile node and the correspondent node may now operate according to thestandard, without being required to read the entire hop-by-hop extensionheader. This is because the router only needs to read as far as therouter alert option field an ignore the remainder to the hop-by-hopextension header.

In summary, a router may handle the internet packet according to FIG. 6as summarised in FIG. 9 and explained as follows:

S20: The router receives the internet packet in accordance with theexample illustrated in FIG. 6.

S22: The router detects whether or not a next header field of theinternet packet includes a hop-by-hop field option. If not then at stepS28, the router processes the internet packet as usual based on thesource and destination addresses in the un-extended header.

S24: If the router detects that the hop-by-hop extension header ispresent, then the router determines whether a router alert header typeis present within the hop-by-hop extension header field, by reading therouter alert field (3-bits according to Ipv6 [4]). If the router alertheader is present then processing proceeds to step S28 and the routerdoes not read the extension header field.

S26: If the router alert header is not detected then, the hop-by-hopextension header is read by the router and processes the headeraccordingly.

S28: If the router alert header is detected or there is no hop-by-hopextension header field present, then the router forwards the internetpacket in accordance with the destination address and does not readfurther the content of the hop-by-hop extension field.

S30: Processing of internet packets by the router continues.

Inter-working Mobile IPV6 with SBLP of IMS in GPRS/UMTS

FIG. 10 provides a simplified diagram of parts of the GPRS/UMTS networkshown in FIG. 4 and configured for communicating data packets on theup-link from the correspondent node CN to the mobile node MN aspreviously discussed with reference to FIG. 5 for down-linkcommunications.

In FIG. 10 a bearer 900 which was initiated by the correspondent node CNusing a PDP context activation is provided for up-link communications tothe mobile node MN. An example of an Internet packet header 902communicated with an Internet packet on the up-link is sent using thebearer 900 through the UTRAN 404, the SGSN 402 to the GGSN 400 andoutward to the foreign network 212. However, within the GGSN 400, theSBLP is provided in order to police access by the CN (mobile userequipment) to the quality of service resources in the UMTS network andfurther out into the external packet data communications network 212.The SBLP 472 operates to effect a policy function as a policy decisionpoint or policy enforcement point in order to prevent theft of serviceattacks by unscrupulous parties. For example, an unscrupulous party maywish to gain access to IP multimedia subsystem services (IMS) eventhough the party has not subscribed to the services. As such, unless theGGSN can recognise a legitimate destination address, then the packetwill be dropped. The destination address is a legitimate addressestablished when the IP session was set up. For the mobile node, thiswill be the home address.

By using the internet packet according to the example shown in FIG. 6for up-link communications, in which the destination mobile's homeaddress is provided in the hop-by-hop extension header, the internetpacket will be allowed to egress from the GGSN in accordance with theSBLP function. Again, by providing the home address as part of a routeralert option header, a potential performance penalty which may resultfor routers within the network having to read the hop-by-hop field maybe reduced.

The operation of the GGSN in accordance with an egress of packets fromthe GPRS network is illustrated in FIG. 11 and summarised as follows:

S30: The GGSN perform egress packet filtering in accordance with adestination address of internet packets received from the plurality ofpacket data bearers. Egress of internet packets is allowed for internetpackets having a legitimate destination address in accordance with aService Based Local Policy (SBLP) function.

S32: Upon receipt of the internet packet illustrated in FIG. 6, the GGSNdetects from the data provided in the hop-by-hop extension header fieldfor the gateway support node a destination home address of a mobilecorrespondent node which is to be the destination of the internetpackets.

S34: If the hop-by-hop extension header field contains a legitimatedestination home address, then at step S35 egress of internet packets isallowed. Otherwise at step S36 the internet packet is dropped.

Various further aspects and features of the present invention aredefined in the appended claims. Various modifications can be made to theembodiments herein described without departing from the scope of thepresent invention.

REFERENCES

-   [1] D. Johnson, C. Parkins, J. Arkko, “Mobility in Ipv6”, Internet    Draft, Internet Engineering Task Force, 20 Jan. 2003.-   [2] R. Steele, C-C Lee and P. Gould, “GSM, cdmaOne and 3G Systems,”    published by Wiley International ISBN 0 471 491853-   [3] S. Deering and R. Hinden, “Internet Protocol (Version 6 (IPv6)    Specification, Request for Comments 2460, Ipv6 standards document,    www.ietf.org/rfc/rfc2460.txt-   [4] C. Partridge and A. Jackson, Ipv6 Router Alert Option, Request    for Comments 2711, Ipv6 standards document,    www.ietf.org/rfc/rfc2711.txt-   [5] UK Patent application numbers 0226289.7, 0222187.7, 0230336.0,    0222161.2, 0230335.2.    Annex 1    GPRS/UMTS Architecture

The terminology and architecture used in FIG. 1 corresponds to that usedfor the UMTS and that proposed for 3G as administered by the 3GPP, moredetails for which may be found in [1]. In FIG. 1, a Gateway GPRS SupportNode (GGSN) is connected to an external Packet Data Network 102, (PDN).The external PDN communicates as packets using the Internet Protocol(IP). An interface 104 between the GGSN and the external network islabelled Gi which has been standardised although further aspects arebeing standardised. Also connected to the GGSN is a Serving GPRS SupportNode (SGSN) 106 via an interface 108 labelled as Gn/Gp which is alsobeing standardised.

The GGSN and the SGSN are two of network components, which are requiredto support GPRS. The GGSN acts as the gateway between the externalpacket data networks (PDN) and the mobile network, which supports GPRS.The GGSN contains sufficient information to route incoming IP datapackets to the SGSN that is serving a particular User Equipment (UE)which is mobile and receives data via a radio access facility providedby the mobile packet radio network. For the example embodiment the radioaccess facility is provided in accordance with the Universal TerrestrialRadio Access Network (UTRAN) system which is specified in accordancewith the 3GPP standard. The SGSN is connected to the GGSN via a Gninterface if the SGSN is within the same Public Land Mobile Network(PLMN), and connected via the Gp interface to GGSNs belonging to otherPLMNs.

An SGSN provides mobility management of UEs which are moving within anarea supported by the mobile radio network. To this end the SGSN isprovided with access to a Home Location Register (HLR) 110. The SGSN isarranged to route data packets to Radio Network Controllers (RNC) 112,114 for communication via the UTRAN radio access facility to mobileusers UE 116, 118. The UTRAN radio access facility is provided usingNode B apparatus 120, 122, 124, 126, 128, which effectively form basestations providing radio coverage for the area served by the mobiletelecommunications network. The interface 130, 132, 134, 136, 138between each RNC 112, 114 and the Node B apparatus 120, 122, 124, 126,128, are labelled lub and conform to an established or evolvingstandard. Similarly the interfaces 140, 142 between the SGSN and eachRNC 112, 114 are labelled as Iu-ps and is an evolving standard.

1. An internet packet comprising a header field, the header fieldincluding a field identifying a source address of the internet packet, afield identifying the destination address of the internet packet and anext header field identifying whether an extension header follows theheader and a type of the extension header, wherein the header fieldidentifies that the extension header includes a hop-by-hop extensionheader, the hop-by-hop extension header including a router alert optionheader indicating that the hop-by-hop extension header is optional for arouter to read, and a value field indicating that the remainder of thehop-by-hop header is provided for a gateway support node of a packetradio network, wherein the remainder of the hop-by-hop extension headerincludes a field providing a home address of a mobile node.
 2. Aninternet packet as claimed in claim 1, wherein the router alert optionheader includes a first field indicating that the hop-by-hop extensionheader is optional, a second field indicating the hop-by-hop option typenumber, and a third value field, the value in the third value fieldindicating that a fourth field provides the home address of a mobilenode.
 3. An internet packet as claimed in claim 2 or 3, wherein thefirst field of the router alert option header is provided as arelatively short field with the effect that a time for a router to readthe first field is reduced with respect to a requirement to read alldata in the hop-by-hop extension header.
 4. An internet packet asclaimed in claim 3, wherein the first field comprises three bits.
 5. Aninternet packet as claimed in claim 4, wherein the three bits are allzeros.
 6. An internet packet as claimed in claims 3, 4 or 5, wherein thesecond field of the router alert option header indicating the hop-by-hopoption type comprises five bits set to a value of five.
 7. An internetpacket as claimed in any preceding claim, wherein the internet packet isa IPv6 internet packet.
 8. An internet packet as claimed in any of claim1 to 7, wherein the home address of the mobile node corresponds to thesource address of the mobile node when associated with a home networkwhen an internet protocol session was initiated.
 9. An internet packetas claimed in any of claims 1 to 7, wherein the home address of themobile node corresponds to the destination address of the mobile nodeassociated with a home network when an internet protocol session wasinitiated.
 10. An internet packet as claimed in any of claims 1 to 9,wherein the packet radio network is a General Packet Radio Servicenetwork, the information for the gateway support node being provided fora Gateway GPRS Support Node of the GPRS network.
 11. A gateway supportnode (GGSN) operable to provide an interface between an external packetdata communications network and a packet radio network, the packet radionetwork providing a plurality of packet data bearers for communicatingthe internet packets with nodes attached to the packet radio network,each of the packet data bearers being defined with respect to a sourcehome address of nodes communicating the internet packets, the gatewaysupport node (GGSN) being operable upon receipt of the internet packetaccording to any of claims 1 to 10, to detect that a next header fieldof the internet packet includes a hop-by-hop extension header, and todetect a router alert option header in the hop-by-hop extension header,and a value field indicating that the remainder of the hop-by-hopextension header is provided for the gateway support node, and upondetecting the value field indicating that the remainder of thehop-by-hop extension header field is for the gateway support node, torecover information from a field provided in the remainder of thehop-by-hop extension header for use in controlling egress and/or ingressof internet packets to the packet radio network in accordance with theinformation, wherein the gateway support node is operable to controlingress of internet packets from the external communications network tothe packet data bearers of the packet radio network, by detecting fromthe information field provided in the remainder of the hop-by-hopextension header a source home address of a mobile correspondent nodecommunicating the internet packets, using the home address to identifythe packet data bearer for communicating the internet packets to acorrespondent node attached to the packet radio network, and allowingingress of the internet packets to the identified packet data bearer.12. A gateway support node as claimed in claim 11, the gateway supportnode being operable to allow ingress of the internet packets if eitherthe address in the source address field of the internet packet or theaddress provided in the field in hop-by-hop extension header for thegateway support node corresponds to a packet data bearer.
 13. A gatewaysupport node as claimed in claim 11 or 12, the gateway support nodebeing operable to perform egress packet filtering in accordance with adestination address of the internet packets received from the pluralityof packet data bearers, egress of the internet packets being allowed forinternet packets having a legitimate destination address, and uponreceipt of the internet packet according to any of claims 1 to 10, todetect from the information data provided in the hop-by-hop extensionheader field for the gateway support node a destination home address ofa mobile correspondent node which is to be the destination of theinternet packets, and to allow egress of the internet packets if thegateway support node recognises the destination home address as alegitimate home address.
 14. A gateway support node as claimed in claim13, the gateway support node being operable to allow egress of theinternet packets if either the address in the destination address fieldof the packet or the address provided in the hop-by-hop extension headerfor the gateway support node is a legitimate destination address.
 15. Agateway support node as claimed in any of claims 11 to 14, wherein thegateway support node is operable as a Gateway GPRS Support Node (GGSN),according to the General Packet Radio System standard.
 16. A packetradio network operable to communicate internet packets between anexternal packet data network and nodes associated with the packet radionetwork, the packet radio network providing a plurality of packet databearers for communicating the internet packets to and/or from the nodesattached to the packet radio network, the packet radio network includinga gateway support node as claimed in any of claims 11 to
 15. 17. Apacket radio network as claimed in claim 16, wherein the packet radionetwork is operable in accordance with the General Packet Radio System(GPRS) standard, the gateway support node being a Gateway GPRS SupportNode (GGSN).
 18. A method of operating a gateway support node tointerface between an external packet data communications network and apacket radio network, the packet radio network providing a plurality ofpacket data bearers for communicating the internet packets with nodesattached to the packet radio network, each of the packet data bearersbeing defined with respect to a source home address of the nodescommunicating the internet packets, the method comprising receiving aninternet packet according to any of claims 1 to 10, detecting that anext header field of the internet packet identifies that an extensionheader includes a hop-by-hop extension header, detecting a router alertoption header and a value field in the hop-by-hop extension headerindicating that the remainder of the hop-by-hop header is provided forthe gateway support node, and upon detecting the value field indicatingthat the remainder of the hop-by-hop extension header field is for thegateway support node recovering from a field provided in the remainderof the hop-by-hop extension header information for use in controllingegress and/or ingress of internet packets to the packet radio network inaccordance with the information, wherein, the controlling the ingress ofinternet packets from the external communications network to the packetdata bearers of the packet radio network in accordance with theinformation, includes detecting from the information provided in theremainder of the hop-by-hop extension header field a source home addressof a mobile correspondent node communicating the internet packets, usingthe home address to identify the packet data bearer for communicatingthe internet packets to a correspondent node attached to the packetradio network, and allowing ingress of the internet packets to theidentified packet data bearer, and otherwise dropping the internetpacket.
 19. A method as claimed in claim 18, the method comprisingperforming egress packet filtering in accordance with a destinationaddress of internet packets received from the plurality of packet databearers, egress of internet packets being allowed for internet packetshaving a legitimate destination address, and upon receipt of internetpackets according to any of claims 1 to 10, detecting from informationprovided in the remainder of the hop-by-hop extension header field forthe gateway support node a destination home address of a mobilecorrespondent node which is to be the destination of the internetpackets, and allowing egress of internet packets if the gateway supportnode recognises the destination home address as a legitimate homeaddress.
 20. A signal representing an internet packet according to anyof claims 1 to
 10. 21. A signal bearing medium, the medium bearing thesignal according to claim
 20. 22. Use of an IPv6 Router Alert optionheader for communicating a source home address of a mobile node to aGateway GPRS Support Node, the router alert option header including afield indicating that the router alert option header containing thesource home address is intended for the Gateway GPRS Support Node.
 23. Acomputer program providing computer executable instructions, which whenloaded on to a data processor configures the data processor to operateas a gateway support node as claimed in any of claims 11 to
 15. 24. Acomputer program having computer executable instructions, which whenloaded on to a data processor causes the data processor to perform amethod according to any of claims 18 or 1,9.
 25. A computer programproduct having a computer readable medium having recorded thereoninformation signals representative of the computer program claimed inclaim 23 or 24.